Retention Of Mechanical Properties In Steel Alloys After Processing And In The Presence Of Stress Concentration Sites

ABSTRACT

This invention is related to retention of mechanical properties in high strength steel at reduced thicknesses and which mechanical property performance is also retained at relatively high strain rates. These new steels can offer advantages for a myriad of applications where reduced sheet thickness is desirable. In addition, the alloys herein are those that retain useful mechanical properties after introduction of a geometric discontinuity and an accompanying stress concentration.

FIELD OF INVENTION

This disclosure is related to retention of mechanical properties in high strength steel at reduced thicknesses and which mechanical property performance is also retained at relatively high strain rates. These new steels can offer advantages for a myriad of applications where reduced sheet thickness is desirable. In addition, the alloys herein are those that retain useful mechanical properties after introduction of a geometric discontinuity and an accompanying stress concentration.

BACKGROUND

Steel is the engineering material of choice where cost, strength, and ductility are major factors. Accordingly, steel continues to be used in a myriad of applications in our daily lives, including in the construction of buildings, appliances, and automobiles. A large variety of steel alloys exist to achieve this range of needs, with targeted property ranges used for these wide ranging applications. Designations are provided for ranges of steel, which fit three distinct classes based upon measured properties, in particular maximum tensile strain and tensile stress prior to failure. These three classes are: Low Strength Steels (LSS), High Strength Steels (HSS), and Advanced High Strength Steels (AHSS). Advanced High Strength Steels (AHSS) are of primary interest for advanced engineering applications, and are classified by tensile strengths greater than 700 MPa and include such types as martensitic steels (MS), dual phase (DP) steels, transformation induced plasticity (TRIP) steels, and complex phase (CP) steels. As the strength level increases the trend in maximum tensile elongation (ductility) of the steel is negative, with decreasing elongation at high tensile strengths. For example, tensile elongation of LSS, HSS and AHSS ranges from 25% to 55%, 10% to 45%, and 4% to 30%, respectively.

An area where steel provides particular engineering advantages is in automobiles, with many different types of steels utilized throughout the car in various locations. Current consumer desires and governmental regulations are pushing automobile manufacturers to design vehicles that attain ever greater fuel efficiency. Automobile designers have identified weight reduction, particularly in the body-in-white structure, to have the greatest potential impact on improving fuel efficiency. The process of reducing automobile weight, known as lightweighting, can be accomplished through reducing the thickness of the body-in-white structure and increasing the geometric complexity of the various parts using high strength, high formability materials. Accordingly, increasingly high strength steels are desired throughout the automobile assembly in order to enable the thickness reduction and weight savings.

Safety must be kept constant or improved during the lightweighting process as well. Automobile highway speed limits are regularly increasing, and consumers expect safety performance to be a major part of automobile design. The body-in-white structure of an automobile is designed to provide a rigid structure that will protect the passenger while traveling at speed and in the case of a collision. During an automobile collision, dynamic loading, rapid deformation, and energy dissipation occurs throughout the automobile and body-in-white structure in particular. The time frame over which this occurs can be 100 ms. High strain rates are observed throughout the body-in-white structure during this time, and materials need to be able to withstand complex loads across a range of strain rates. For instance, a low speed collision that occurs in a parking lot would result in a lower strain rate for body-in-white than would a collision at highway speeds. The mechanical properties of materials for the body-in-white structure are measured by many means, including uniaxial tensile testing, across this range of strain rates such that their response during a collision can be predicted and design considerations taken into account. High strain rates can result in a change in mechanical properties, limiting the maximum lightweighting that automobile designers are able to achieve by requiring additional thickness to maintain safety under high strain rate conditions.

As advances in engineering and technology occur, there is an increasing drive to the small scale. Consumers, and by extension engineers/designers, are regularly searching for products that are size efficient. Consumers seek out products that accomplish the needed task while occupying the smallest volume possible. A good example of this phenomenon can be found in the electronics industry, where cell phones, tablets, and other devices are regularly reduced in size with consecutive design iterations. With the drive of products to smaller and smaller sizes, the demands on engineering materials that the products are made from increase dramatically. As the overall size of a part decreases, defects that are inherent in everyday manufacturing processes can result in significant reductions in material properties. High strength materials are particularly impacted by the reduction of part size to the small or very small due to the complex and often specialized processing required to achieve those properties.

Martensitic steels, for example, provide excellent strength yet require a quench as a final processing step to create the necessary microstructure. Quenching is difficult to control at a small scale and may potentially cause unacceptable distortion in small parts. Final processing may not be performed on the final part geometry but rather on sheet or foils in some applications. For thermally sensitive materials such as martensitic steels, thermal exposure during cutting to produce the final part may detrimentally alter the microstructure and compromise properties. Geometry effects also play a greater role in mechanical properties of ductile materials at the small scale, with the effects of stress concentrators, grain size, and thickness adversely changing the material's mechanical response to stress. Due to these facts, expensive engineering materials are often required for uses on small scale that are either thermally insensitive or have simple processing such as low alloyed or pure materials. Engineers would prefer to not use exotic materials for these applications; however everyday engineering materials are often unavailable for use at reduced thicknesses resulting in the slow adoption of smaller devices due to prohibitive cost and processing requirements.

SUMMARY

In one embodiment, the present invention is directed at a method to retain mechanical properties in a metallic sheet alloy at reduced thickness comprising supplying a metal alloy comprising at least 70 atomic % iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu, or C, melting said alloy, cooling at a rate of <250 K/s, and solidifying to a thickness of 25.0 mm up to 500 mm. This is followed by processing the alloy into sheet form with thickness T₁ with the sheet having a total elongation of X₁ (%), an ultimate tensile strength of Y₁ (MPa), and a yield strength of Z₁ (MPa). This is then followed by further processing the alloy into a second sheet with reduction in thickness T₂<T₁ with the second sheet having a total elongation of X₂=X₁±10%, an ultimate tensile strength of Y₂=Y₁±50 MPa, and a yield strength of Z₂=Z₁±100 MPa.

In another embodiment the present invention relates to a method to retain mechanical properties in a metallic sheet alloy at relatively high strain rates comprising supplying a metal alloy comprising at least 70 atomic % iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu, or C and melting said alloy and cooling at a rate of <250 K/s and solidifying to a thickness of 25.0 mm up to 500 mm. This is then followed by processing the alloy into sheet form with thickness from 1.2 mm to 10.0 mm with the sheet having a total elongation of X₁ (%), an ultimate tensile strength of Y₁ (MPa), and a yield strength of Z₁ (MPa) when tested at a strain rate S₁. This is then followed by deforming the sheet from the alloy at a strain rate S₂>S₁ with the sheet having a total elongation of X₃=X₁±7%, ultimate tensile strength Y₃=Y₁±200 MPa, and yield strength Z₃=Z₁±50 MPa.

In yet another embodiment the present invention is directed at A method to retain mechanical properties in a metallic sheet alloy comprising supplying a metal alloy comprising at least 70 atomic % iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu, or C and melting said alloy and cooling at a rate of <250 K/s and solidifying to a thickness of 25.0 mm up to 500 mm. This is then followed by processing the alloy into sheet form with thickness from 1.2 mm to 10.0 mm with the sheet having a total elongation of X₁ (%), an ultimate tensile strength of Y₁ (MPa), and a yield strength of Z₁ (MPa). Then, one may introduce stress concentration sites and then deform the sheet from the alloy with the sheet having a total elongation of X₄≤0.2X₁ (%), an ultimate tensile strength Y₄≤0.5Y₁ (MPa), and a yield strength Z₄≥0.6Z₁ (MPa).

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description below may be better understood with reference to the accompanying FIG.s which are provided for illustrative purposes and are not to be considered as limiting any aspect of this invention.

FIG. 1 Summary of novel ductility achievement in alloys herein at reduced length scales.

FIG. 2 Summary of novel ductility achievement in the alloys herein at high strain rates.

FIG. 3 Summary of maintained ductility in the alloys herein with introduced stress concentration sites such as edge notches.

FIG. 4 Yield strength and ultimate tensile strength as a function of Alloy 2 sheet thickness.

FIG. 5 Tensile elongation as a function of Alloy 2 sheet thickness.

FIG. 6 Comparison of stress-strain curves for Alloy 2 sheet with different thicknesses.

FIG. 7 Effect of sheet thickness on tensile elongation of samples from various alloys.

FIG. 8 Effect of sheet thickness on yield strength in samples from various alloys.

FIG. 9 Effect of sheet thickness on ultimate tensile strength in samples from various alloys.

FIG. 10 SEM images of the microstructure in the center of Alloy 1 sheet samples with various thicknesses; a) 0.7 mm thick cold rolled sheet, b) 0.7 mm thick cold rolled and annealed sheet, c) 0.5 mm thick cold rolled sheet, and d) 0.5 mm thick cold rolled and annealed sheet.

FIG. 11 SEM images of the microstructure in the center of Alloy 2 sheet samples with various thicknesses; a) 1.0 mm thick cold rolled sheet, b) 1.0 mm thick cold rolled and annealed sheet, c) 0.5 mm thick cold rolled sheet, d) 0.5 mm thick cold rolled and annealed sheet, e) 0.2 mm thick cold rolled sheet, and f) 0.2 mm thick cold rolled and annealed sheet.

FIG. 12 SEM images of the microstructure in the center of Alloy 27 sheet samples with various thicknesses; a) 0.8 mm thick cold rolled sheet, b) 0.8 mm thick cold rolled and annealed sheet, c) 0.5 mm thick cold rolled sheet, d) 0.5 mm thick cold rolled and annealed sheet, e) 0.4 mm thick cold rolled sheet, and f) 0.4 mm thick cold rolled and annealed sheet.

FIG. 13 SEM images of the microstructure in the center of Alloy 37 sheet samples with various thicknesses; a) 1.4 mm thick cold rolled sheet, b) 1.4 mm thick cold rolled and annealed sheet, c) 0.5 mm thick cold rolled sheet, d) 0.5 mm thick cold rolled and annealed sheet, e) 0.3 mm thick cold rolled sheet, and f) 0.3 mm thick cold rolled and annealed sheet.

FIG. 14 Schematic illustration of the ASTM D 638 Type V tensile specimen geometry; all dimensions are in millimeters.

FIG. 15 Schematic diagram of the direct tension split Hopkinson bar (SHB) device.

FIG. 16 Effect of strain rate on the tensile elongation at fracture for Alloy 2 sheet.

FIG. 17 Bright-field TEM micrographs of microstructure in gauge section of the sample from Alloy 2 sheet tested at strain rate of 1200 s⁻¹; a) lower magnification image, b) higher magnification image.

FIG. 18 Bright-field TEM micrographs of microstructure in gauge section of the sample from Alloy 2 sheet tested at strain rate of 500 s⁻¹; a) lower magnification image, b) higher magnification image.

FIG. 19 Bright-field TEM micrographs of microstructure in gauge section of the sample from Alloy 2 sheet tested at strain rate of 100 s⁻¹; a) lower magnification image, b) higher magnification image.

FIG. 20 Bright-field TEM micrographs of microstructure in gauge section of the sample from Alloy 2 sheet tested at strain rate of 10 s⁻¹; a) lower magnification image, b) higher magnification image.

FIG. 21 Bright-field TEM micrographs of microstructure in gauge section of the sample from Alloy 2 sheet tested strain rate of 0.7 s⁻¹; a) lower magnification image, b) higher magnification image.

FIG. 22 Bright-field TEM micrographs of microstructure in gauge section of the sample from Alloy 2 sheet tested at strain rate of 0.0007 s⁻¹; a) lower magnification image, b) higher magnification image.

FIG. 23 Feritscope measurements at the gauge section of the samples from Alloy 2 sheet tested at different strain rates.

FIG. 24 Schematic illustration of the notched tensile sample.

FIG. 25 Notch diameter with a constant depth of 0.5 mm effect; a) on tensile elongation and b) on ultimate tensile strength of the sheet from Alloy 2.

FIG. 26 Half circle notch diameter effect; a) on tensile elongation and b) on ultimate tensile strength of the sheet from Alloy 2.

FIG. 27 SEM images of the fracture surface in the Sample 1 from Alloy 2 with a notch of 1 mm in diameter; a) in the center of the fracture cross section, b) near the edge of the fracture cross section.

FIG. 28 SEM images of the fracture surface in the Sample 2 from Alloy 2 with a notch of 6 mm in diameter; a) in the center of the fracture cross section, b) near the edge of the fracture cross section.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The retention of mechanical properties in the alloys herein at reduced thickness and relatively high strain rates is illustrated in FIG. 1 and FIG. 2. FIG. 1 represents a summary on mechanical property retention in the alloys herein when reduced in thickness. In Step 1 in FIG. 1, the starting condition is to supply a metal alloy. This metal alloy will preferably comprise at least 70 atomic % iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu, or C. The alloy chemistry is melted, cooled at a rate of <250 K/s, and solidified to a thickness of 25.0 mm and up to and including 500 mm. The casting process can be done in a wide variety of processes including ingot casting, bloom casting, continuous casting, thin slab casting, thick slab casting, thin strip casting, belt casting etc. Preferred methods would be continuous casting in sheet form by thin slab casting, thick slab casting, and thin strip casting. Preferred alloys exhibit a fraction of austenite (y-Fe) at least 10 volume percent up to 100 volume percent and all increments in between. The alloy is then processed into sheet form with a thickness T₁ that is in the range of 1.2 mm to 10.0 mm, and therefore includes thicknesses of 1.2 mm, 1.3 mm. 1.4 mm 1.5 mm. 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm, 3.0 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm, 3.6 mm, 3.7 mm, 3.8 mm, 3.9 mm, 4.0 mm, 4.1 mm, 4.2 mm, 4.3 mm, 4.4 mm, 4.5 mm, 4.6 mm, 4.7 mm, 4.8 mm, 4.9 mm and 5.0 mm, 5.1 mm, 5.2 mm, 5.3 mm. 5.4 mm. 5.5 mm, 5.6 mm, 5.7 mm, 5.8 mm, 5.9 mm, 6.0 mm, 6.1 mm, 6.2 mm, 6.3 mm, 6.4 mm, 6.5 mm, 6.6 mm, 6.7 mm, 6.8 mm, 6.9 mm, 7.0 mm, 7.1 mm, 7.2 mm, 7.3 mm, 7.4 mm, 7.5 mm, 7.6 mm, 7.7 mm, 7.8 mm, 7.9 mm, 8.0 mm, 8.1 mm, 8.2 mm, 8.3 mm, 8.4 mm, 8.5 mm, 8.6 mm, 8.7 mm, 8.8 mm, 8.9 mm, 9.0 mm, 9.1 mm, 9.2 mm, 9.3 mm, 9.4 mm, 9.5 mm, 9.6 mm, 9.7 mm, 9.8 mm, 9.9 mm and 10.0 mm.

The steps to produce this sheet at thickness T₁ from the cast product can vary depending on specific manufacturing routes and specific targeted goals. As an example, consider thick slab casting as one process route to get to sheet of this targeted thickness. The alloy would be cast going through a water cooled mold typically in a thickness range of 150 to 300 mm in thickness. The cast ingot after cooling would then be preferably prepared for hot rolling which may involve some surface treatment to remove surface defects including oxides. The ingot would then go through a roughing mill hot roller which may involve several passes resulting in a transfer bar slab typically from 15 to 100 mm in thickness. This transfer bar would then go through successive/tandem hot rolling finishing stands to produce hot band coils which have a thickness T₁ in the above referenced range from 1.2 mm to 10.0 mm.

Another example would be to preferably process the cast material through a thin slab casting process. In this case, after casting typically forms 35 to 150 mm in thickness by going through a water cooled mold, the newly formed slab goes directly to hot rolling without cooling down with auxiliary tunnel furnace or induction heating applied to bring the slab directly up to targeted temperature. The slab is then hot rolled directly in multi-stand finishing mills which are preferably from 1 to 7 in number. After hot rolling, the strip is rolled into hot band coils with thickness T₁ in the above referenced range of 1.2 mm to 10.0 mm in thickness. Note that bloom casting would be similar to the examples above but higher thickness might be cast typically from 200 to 500 mm thick and initial breaker steps would be needed to reduce initial cast thickness to allow it to go through a hot rolling roughing mill. Strip casting would be similar but lower thickness might be cast of T₁ having a value of 1.2 mm to 10.0 mm in thickness with preferably only one hot rolling stand directly after casting.

Accordingly, the specific process in going from the slab material in Step 1 to a preferred thickness T₁ of 1.2 mm to 10 mm and then in Step 2 to a preferred thickness in the range of 0.2 mm to less than 1.2 mm may include hot rolling, cold rolling, and/or cold rolling followed by annealing. Accordingly, in Step 2, the alloy thickness may preferably be 0.2 mm, 0.3 mm, 0.4 mm. 0.5 mm. 0.6 mm. 0.7 mm. 0.8 mm. 0.9 mm, 1.0 mm 1.1 mm up to by not including 1.2 mm. Hot rolling is generally used to provide a preferred thickness from 1.2 mm to 10.0 mm and is typically done in roughing mills, finishing mills, and/or Steckel mills. Cold rolling is preferred in Steps 1 and/or Step 2 and is generally done using tandem mills, Z-mills, and/or reversing mills. The cold rolled material depending on property targets may be annealed to restore the ductility lost from the cold rolling process either partially or with restoration of ductility. Typically as cold rolling proceeds and higher amounts of gauge reduction occurs, ductility is reduced and cold rolling will continue until or just before cracking is observed. Restoration of the tensile ductility of the cold rolled sheet generally occurs with heat treatments at 700° C. and above. Once the sheet is formed with thickness T₁ specified in Step 2, the sheet will then exhibit a total elongation of X₁ (%), an ultimate tensile strength of Y₁ (MPa), and a yield strength of Z₁ (MPa). Preferred properties for alloys herein in Step 2 would be tensile elongation from 12 to 80%, ultimate tensile strength values from 700 to 2100 MPa, and yield strength is in a range from 250 to 1500 MPa.

In Step 3, the alloy is preferably cold rolled and annealed in similar manner as in Step 2 to thickness T₂<T₁. In Step 3, comparing said alloy in Step 1 and after Step 2, the total elongation is maintained at the level where the total elongation X₂=X₁±10%, Y₂=Y₁±50 MPa, and Z₂=Z₁±100 MPa. The thickness of the alloy in Step 3 is identified as T₂ and is less than the thickness T₁ in Step 2. The preferred properties of the alloy in Step 3 are as follows: X₂=2 to 90%; Y₂=650 MPa to 2150 MPa and Z₂=150 MPa to 1600 MPa.

FIG. 2 shows a summary on ductility retention of the present disclosure in the alloys herein at relatively high strain rates, that is where the alloys experience a strain rate of S₂ of >0.007 to 1200 s⁻¹. Step 1 and Step 2 are identical to that described above in relation to FIG. 1. Once the sheet is formed with thickness from 1.2 mm to 10.0 mm, the sheet will then exhibit a total elongation of X₁ (%), an ultimate tensile strength of Y₁ (MPa), and a yield strength of Z₁ (MPa) when tested at strain rate S₁, which is preferably at or below 0.007 s⁻¹ and in the range from 0.007 to 0.0001 s⁻¹ Preferred properties for this alloy would be tensile elongation from 12 to 80%, ultimate tensile strength values from 700 to 2100 MPa, and yield strength is in a range from 250 to 1500 MPa. In Step 3, the sheet with thickness from 0.2 mm to less than 1.2 mm is such that when deformed at an engineering strain rate S₂>S₁ and the alloy exhibits X₃=X₁±7%, ultimate tensile strength Y₃=Y₁±200 MPa, and yield strength Z₃=Z₁±50 MPa. The preferred properties of the alloy in Step 3 are as follows: X₃=5 to 87%; Y₃=500 MPa to 2300 MPa, and Z₃=200 MPa to 1550 MPa.

Alloys herein are also shown to avoid brittle fracture when stress concentration sites are introduced such as notches at the sheet edge. A stress concentration site herein is a location on the alloy sheet where stress can be concentrated, including but not limited to geometric discontinuities, such as a notch, hole, cut in the surface, crack, chipped portion, dent, etc. FIG. 3 shows a summary on how changes in mechanical properties are retained in the alloys herein with the introduction of stress concentration sites such as edge notches. Once the sheet is formed with thickness from 1.2 mm to 10.0 mm in Step 2, the sheet will then exhibit a total elongation of X₁ (%), an ultimate tensile strength of Y₁ (MPa), and a yield strength of Z₁ (MPa). Preferred properties for this alloy would again be tensile elongation from 12 to 80%, ultimate tensile strength values from 700 to 2100 MPa, and yield strength is in a range from 250 to 1500 MPa. In Step 3, the sheet that experiences a stress concentration is capable of exhibiting the following in response to a deformation: X₄≥0.2X₁ (%), an ultimate tensile strength Y₄≥0.5Y₁ (MPa), and a yield strength Z₄≥0.6Z₁ (MPa). The preferred properties of the alloy in Step 3 are as follows: X₄≥2.4%; Y₄≥350 MPa, and Z₄≥150 MPa.

Alloys

The chemical composition of the alloys herein is shown in Table 1 which provides the preferred atomic ratios utilized.

TABLE 1 Chemical Composition of Alloys (Atomic %) Alloy Fe Cr Ni Mn Si Cu C Alloy 1 75.75 2.63 1.19 13.86 5.13 0.65 0.79 Alloy 2 74.75 2.63 1.19 14.86 5.13 0.65 0.79 Alloy 3 77.31 2.63 8.49 5.00 5.13 0.65 0.79 Alloy 4 77.14 2.63 6.49 7.17 5.13 0.65 0.79 Alloy 5 76.24 2.63 4.49 10.07 5.13 0.65 0.79 Alloy 6 75.34 2.63 2.49 12.97 5.13 0.65 0.79 Alloy 7 78.92 2.63 6.49 5.39 5.13 0.65 0.79 Alloy 8 77.34 2.63 4.49 8.97 5.13 0.65 0.79 Alloy 9 75.77 2.63 2.49 12.54 5.13 0.65 0.79 Alloy 10 75.90 2.63 3.74 11.16 5.13 0.65 0.79 Alloy 11 77.73 2.63 3.74 9.33 5.13 0.65 0.79 Alloy 12 79.57 2.63 3.74 7.49 5.13 0.65 0.79 Alloy 13 75.97 2.63 3.74 10.09 5.13 1.65 0.79 Alloy 14 77.80 2.63 3.74 8.26 5.13 1.65 0.79 Alloy 15 79.64 2.63 3.74 6.42 5.13 1.65 0.79 Alloy 16 76.88 2.63 3.74 9.18 5.13 1.65 0.79 Alloy 17 76.83 2.63 3.74 9.85 5.13 1.03 0.79 Alloy 18 76.57 2.63 3.06 10.17 5.13 1.65 0.79 Alloy 19 76.52 2.63 3.06 10.84 5.13 1.03 0.79 Alloy 20 78.02 1.13 3.06 10.84 5.13 1.03 0.79 Alloy 21 80.02 1.13 3.06 10.84 3.13 1.03 0.79 Alloy 22 76.70 2.63 3.40 10.01 5.13 1.34 0.79 Alloy 23 76.20 3.13 3.40 10.01 5.13 1.34 0.79 Alloy 24 75.70 3.63 3.40 10.01 5.13 1.34 0.79 Alloy 25 77.70 2.63 3.40 10.01 4.13 1.34 0.79 Alloy 26 75.70 2.63 3.40 10.01 6.13 1.34 0.79 Alloy 27 77.20 2.63 3.40 10.01 4.13 1.34 1.29 Alloy 28 75.20 2.63 3.40 10.01 6.13 1.34 1.29 Alloy 29 76.98 2.88 3.40 10.01 4.63 1.34 0.76 Alloy 30 77.23 2.88 3.15 10.01 4.63 1.34 0.76 Alloy 31 77.48 2.88 2.90 10.01 4.63 1.34 0.76 Alloy 32 77.73 2.88 2.65 10.01 4.63 1.34 0.76 Alloy 33 77.98 2.88 2.40 10.01 4.63 1.34 0.76 Alloy 34 74.59 2.61 0.00 15.17 3.59 1.86 2.18 Alloy 35 82.22 3.69 9.94 0.00 2.26 0.37 1.52 Alloy 36 76.17 8.64 0.90 11.77 0.00 1.68 0.84 Alloy 37 82.77 4.41 6.66 3.19 1.14 1.16 0.67 Alloy 38 76.55 0.78 0.72 14.43 3.42 0.42 3.68 Alloy 39 81.44 0.00 4.42 10.33 2.87 0.00 0.94 Alloy 40 81.00 1.22 0.89 13.45 2.66 0.78 0.00 Alloy 41 81.68 2.24 3.25 9.87 0.00 1.55 1.41 Alloy 42 78.47 3.16 5.57 7.43 3.70 0.51 1.16 Alloy 43 79.73 3.34 7.02 4.95 3.22 0.46 1.28 Alloy 44 81.47 3.69 10.69 0.00 2.26 0.37 1.52 Alloy 45 80.72 3.69 11.44 0.00 2.26 0.37 1.52 Alloy 46 81.47 3.69 9.94 0.00 2.26 1.12 1.52 Alloy 47 80.72 3.69 9.94 0.00 2.26 1.87 1.52 Alloy 48 81.00 3.69 9.94 0.00 3.70 0.51 1.16 Alloy 49 82.84 1.85 9.94 0.00 3.70 0.51 1.16 Alloy 50 84.69 0.00 9.94 0.00 3.70 0.51 1.16 Alloy 51 82.30 3.69 4.97 3.67 3.70 0.51 1.16 Alloy 52 81.00 3.69 4.97 4.97 3.70 0.51 1.16 Alloy 53 79.70 3.69 4.97 6.27 3.70 0.51 1.16 Alloy 54 83.52 3.69 4.97 3.67 2.26 0.37 1.52 Alloy 55 82.22 3.69 4.97 4.97 2.26 0.37 1.52 Alloy 56 80.92 3.69 4.97 6.27 2.26 0.37 1.52

As can be seen from Table 1, the alloys herein comprise, consist essentially of, or consist of iron based metal alloys, having greater than 70 at. % Fe, and at least four or more elements selected from the following six (6) elements: Si, Mn, Cr, Ni, Cu, and C. The level of impurities of other elements are in the range of 0 to 5000 ppm. Accordingly, if there is 5000 ppm of an element other than the selected elements identified, the level of such selected elements may then in combination be present at a lower level to account for the 5000 ppm impurity, such that the total of all elements present (selected elements and impurities) is 100 atomic percent.

With regards to the above, and as can be further seen from Table 1, preferably, when Fe is present at a level of greater than 70 at. %, and one then selects the four or more elements from the indicated six (6) elements, or selects five or more elements, or selects all six elements to provide a formulation of elements that totals 100 atomic percent. The preferred levels of the elements, if selected, may fall in the following ranges: Si (1.14 to 6.13), Mn (3.19 to 15.17), Cr (0.78 to 8.64); Ni (0.9 to 11.44), Cu (0.37 to 1.87), and C (0.67 to 3.68). Accordingly, it can be appreciated that if four (4) elements are selected, two of the six elements are not selected and may be excluded. If five (5) elements are selected, one of the elements of the six can be excluded. Moreover, a particularly preferred level of Fe is in the range of 73.95 to 84.69 at. %. Again, the level of impurities of other elements are preferably controlled in the range of 0 to 5000 ppm (0 to 0.5 wt %).

Laboratory Slab Casting

Alloys were weighed out into 3,000 to 3,400 gram charges according to the atomic ratios in Table 1 using commercially available ferroadditive powders and a base steel feedstock with known chemistry. As alluded to above, impurities can be present at various levels depending on the feedstock used. Impurity elements would commonly include the following elements; Al, Co, N, P, Ti, Mo, W, Ga, Ge, Sb, Nb, Zr, O, Sn, Ca, and S which if present would be in the range from 0 to 5000 ppm (parts per million) (0 to 0.5 wt %) at the expense of the desired elements noted above. Preferably, the level of impurities is controlled to fall in the range of 0 to 3000 ppm (0.3 wt %).

Charges were loaded into a zirconia coated silica crucible which was placed into an Indutherm VTC800V vacuum tilt casting machine. The machine then evacuated the casting and melting chambers and flushed with argon to atmospheric pressure twice prior to casting to prevent oxidation of the melt. The melt was heated with a 14 kHz RF induction coil until fully molten, approximately from 5 to 7 minutes depending on the alloy composition and charge mass. After the last solids were observed to melt it was allowed to heat for an additional 30 to 45 seconds to provide superheat and ensure melt homogeneity. The casting machine then evacuated the chamber and tilted the crucible and poured the melt into a water cooled copper die. The melt was allowed to cool under vacuum for 200 seconds before the chamber was filled with argon to atmospheric pressure.

Laboratory casting corresponds to Step 1 in FIG. 1, FIG. 2 and FIG. 3 and provides slabs with thickness of 50 mm. Depending on equipment capability, slab thickness in Step 1 can vary from 25.0 to 500 mm.

Thermal Analysis

A sample of between 50 and 150 mg from each alloy herein was taken in the as-cast condition. This sample was heated to an initial ramp temperature between 900° C. and 1300° C. depending on alloy chemistry, at a rate of 40° C./min. Temperature was then increased at 10° C./min to a max temperature between 1425° C. and 1515° C. depending on alloy chemistry. Once this maximum temperature was achieved, the sample was cooled at a rate of 10° C./min back to the initial ramp temperature before being reheated at 10° C./min to the maximum temperature. Differential Scanning calorimetry (DSC) measurements were taken using a Netzsch Pegasus 404 DSC through all four stages of the experiment, and this data was used to determine the solidus and liquidus temperatures of each alloy, which are in a range from 1102 to 1505° C. (Table 2). Depending on alloys chemistry, liquidus-solidus gap varies from 31 to 138° C. Thermal analysis provides information on maximum temperature for the following hot rolling processes that varies depending on alloy chemistry.

TABLE 2 Thermal Analysis of Selected Alloys Solidus Liquidus Melting Gap Alloy (° C.) (° C.) (° C.) Alloy 1 1390 1448 58 Alloy 2 1398 1446 49 Alloy 3 1403 1456 53 Alloy 4 1411 1456 45 Alloy 5 1391 1448 57 Alloy 6 1384 1442 58 Alloy 7 1407 1462 55 Alloy 8 1400 1452 52 Alloy 9 1386 1444 59 Alloy 10 1375 1444 70 Alloy 11 1392 1453 61 Alloy 12 1393 1459 67 Alloy 13 1374 1441 67 Alloy 14 1386 1453 67 Alloy 15 1401 1459 57 Alloy 16 1400 1453 53 Alloy 17 1397 1453 56 Alloy 18 1399 1452 53 Alloy 19 1400 1452 52 Alloy 20 1401 1454 53 Alloy 21 1409 1467 57 Alloy 22 1396 1452 56 Alloy 23 1394 1450 56 Alloy 24 1404 1454 49 Alloy 25 1405 1460 55 Alloy 26 1372 1440 68 Alloy 27 1383 1454 70 Alloy 28 1369 1430 61 Alloy 29 1420 1458 38 Alloy 30 1412 1459 47 Alloy 31 1431 1462 31 Alloy 32 1408 1460 52 Alloy 33 1415 1462 48 Alloy 34 1358 1445 88 Alloy 35 1458 1496 39 Alloy 36 1406 1488 82 Alloy 37 1462 1502 41 Alloy 38 1294 1432 138 Alloy 39 1438 1491 53 Alloy 40 1425 1481 56 Alloy 41 1438 1494 56 Alloy 42 1442 1481 39 Alloy 43 1460 1493 33 Alloy 44 1458 1500 42 Alloy 45 1465 1505 39 Alloy 46 1456 1498 42 Alloy 47 1453 1492 39 Alloy 48 1456 1496 40 Alloy 49 1472 1504 32 Alloy 50 1456 1500 43 Alloy 51 1451 1491 40 Alloy 52 1430 1480 51 Alloy 53 1442 1482 40 Alloy 54 1447 1489 42 Alloy 55 1450 1490 40 Alloy 56 1447 1488 41

Laboratory Hot Rolling

The alloys herein were preferably processed into a laboratory hot band by hot rolling of laboratory slabs at high temperatures. Laboratory alloy processing is developed to simulate the hot band production from slabs produced by continuous casting. Industrial hot rolling is performed by heating a slab in a tunnel furnace to a target temperature, then passing it through either a reversing mill or a multi-stand mill or a combination of both to reach the target gauge. During rolling on either mill type, the temperature of the slab is steadily decreasing due to heat loss to the air and to the work rolls so the final hot band is formed at a reduced temperature. This is simulated in the laboratory by heating in a tunnel furnace to between 1100° C. and 1250° C., then hot rolling. The laboratory mill is slower than industrial mills causing greater loss of heat during each hot rolling pass so the slab is reheated for 4 minutes between passes to reduce the drop in temperature, the final temperature at target gauge when exiting the laboratory mill commonly is in the range from 800° C. to 1000° C., depending on furnace temperature and final thickness.

Prior to hot rolling, laboratory slabs were preheated in a Lucifer EHS3GT-B18 furnace. The furnace set point varies between 1100° C. to 1250° C., depending on alloy melting point and point in the hot rolling process, with the initial temperatures set higher to facilitate higher reductions, and later temperatures set lower to minimize surface oxidation on the hot band. The slabs were allowed to soak for 40 minutes prior to hot rolling to ensure they reach the target temperature and then pushed out of the tunnel furnace into a Fenn Model 061 2 high rolling mill. The 50 mm casts are hot rolled for 5 to 10 passes though the mill before being allowed to air cool. Final thickness ranges after hot rolling are preferably from 1.8 mm to 4.0 mm with variable reduction per pass ranging from 20% to 50%.

Tensile specimens were cut from laboratory hot band using wire EDM. Tensile properties were measured on an Instron mechanical testing frame (Model 3369), utilizing Instron's Bluehill control and analysis software. Samples were tested under displacement control at a constant displacement rate of 0.036 mm/s, which resulted in sample strain rates, calculated from video strain measurements, ranging from 4.4×10⁻⁴ s⁻¹ to 6.8×10⁻³ s⁻¹, depending on several factors including, but not always limited to mechanical compliance, sample slippage, and settling of the wedge action grips used.

Tensile properties of the alloys in the hot rolled condition with a thickness from 1.8 to 2.3 mm are listed in Table 3 including magnetic phases volume percent (Fe %) that was measured by Feritscope. The ultimate tensile strength values may vary from 913 to 2011 MPa with tensile elongation from 13.0 to 69.5%. The yield strength is in a range from 250 to 1313 MPa. Mechanical properties of the hot band from steel alloys herein depend on alloy chemistry, processing conditions, and material mechanistic response to the processing conditions. The relative magnetic phases volume percent was measured by Feritscope with the magnetic phases volume percent of 0.1 to 64.9 Fe % in a hot band depending on alloy chemistry. Note that the Table 3 properties correspond to Step 2 of FIG. 1, FIG. 2, and FIG. 3. Further processing of the hot band can additionally occur through cold rolling and annealing as shown for example in Case Example 1.

TABLE 3 Hot Band Tensile Properties of Alloys Ultimate Average Magnetic Tensile Tensile Yield Phases Volume Elongation Strength Strength Percent Alloy (%) (MPa) (MPa) (Fe %) Alloy 1 51.4 1248 294 1.7 49.2 1253 310 31.2 1093 396 Alloy 2 57.6 1175 311 1.3 58.6 1209 294 56.6 1167 302 Alloy 3 55.4 1163 330 3.2 59.5 1154 373 58.1 1165 347 Alloy 4 59.8 1220 342 0.3 51.6 1241 338 55.5 1245 375 54.6 1324 377 Alloy 5 54.3 1248 325 0.5 53.1 1218 313 50.6 1258 304 54.1 1242 331 Alloy 6 58.3 1212 330 0.4 53.7 1212 283 58.7 1193 315 Alloy 7 28.1 1508 333 10.4 28.5 1516 331 26.0 1520 317 Alloy 8 41.2 1343 330 0.9 32.8 1281 328 45.7 1387 336 41.4 1375 328 Alloy 9 48.1 1248 300 1.4 50.5 1293 304 52.0 1280 303 Alloy 10 58.5 1229 379 2.7 57.8 1223 384 59.0 1220 389 Alloy 11 45.3 1411 360 0.8 40.2 1460 359 41.3 1429 325 47.1 1448 347 Alloy 12 31.3 1624 250 1.5 31.7 1581 304 28.7 1610 319 Alloy 13 57.1 1101 358 0.1 66.1 1120 362 68.5 1114 362 60.1 1120 350 Alloy 14 45.1 1371 354 0.4 40.6 1403 363 42.3 1403 364 46.9 1379 341 Alloy 15 26.2 1579 295 1.6 25.2 1593 264 24.6 1588 302 Alloy 16 54.8 1239 379 0.2 58.5 1207 341 55.8 1207 359 Alloy 17 51.3 1270 354 0.6 50.1 1328 384 Alloy 18 58.8 1224 384 0.3 56.1 1245 390 50.7 1190 365 Alloy 19 47.4 1263 348 0.4 50.7 1260 362 51.8 1277 363 Alloy 20 40.1 1337 376 0.3 43.9 1343 375 44.7 1328 394 Alloy 21 45.2 1277 327 0.5 46.1 1318 340 54.2 1310 325 Alloy 22 49.6 1272 369 0.3 54.9 1275 354 54.8 1271 319 52.4 1297 340 Alloy 23 53.5 1246 344 0.3 55.9 1226 359 51.2 1232 346 52.7 1228 375 Alloy 24 57.0 1209 356 0.2 54.6 1202 348 55.1 1207 363 56.9 1225 338 Alloy 25 53.4 1227 357 0.4 56.5 1249 325 54.5 1214 345 49.5 1220 343 Alloy 26 49.0 1319 340 0.5 48.4 1320 344 50.5 1304 331 51.1 1296 346 Alloy 27 56.5 967 404 0.1 54.5 956 421 67.6 979 417 52.0 942 390 Alloy 28 50.4 1121 442 0.4 49.8 1088 407 51.8 1116 423 Alloy 29 56.0 1229 422 4.2 56.3 1247 409 54.6 1226 405 50.0 1196 421 56.3 1199 412 53.3 1205 402 Alloy 30 52.1 1271 421 5.5 51.4 1284 416 50.6 1269 407 53.9 1248 418 49.9 1237 399 54.8 1241 407 Alloy 31 48.6 1326 379 6.5 51.3 1323 390 51.6 1293 372 51.4 1314 374 Alloy 32 49.5 1347 383 5.7 47.0 1367 388 47.9 1341 381 47.8 1391 431 Alloy 33 44.8 1373 372 7.3 42.3 1392 381 40.7 1388 381 Alloy 34 65.9 963 515 0.3 58.7 954 485 62.1 970 545 Alloy 35 19.6 2000 533 43.3 22.3 1976 511 19.8 1995 526 Alloy 36 60.1 1091 439 2.0 61.0 1114 469 59.4 1137 481 Alloy 37 13.8 1572 649 56.4 14.1 1619 711 14.6 1610 692 Alloy 38 58.9 1105 531 0.7 61.4 1108 524 58.6 1106 511 Alloy 39 51.0 1317 354 8.2 50.5 1334 370 50.5 1325 368 Alloy 40 47.9 1374 330 5.8 48.8 1336 317 41.5 1362 321 Alloy 41 51.1 963 472 5.2 48.4 913 463 Alloy 42 61.6 1081 440 7.0 69.5 1098 450 64.3 1070 440 67.2 1081 438 62.2 1082 439 Alloy 43 44.5 1176 440 16.6 35.0 1073 447 38.4 1136 447 36.8 1140 454 Alloy 44 23.9 1858 577 40.5 24.5 1852 624 24.9 1866 685 23.1 1841 672 Alloy 45 32.5 1758 439 32.4 28.9 1733 408 26.9 1746 442 26.6 1725 417 Alloy 46 21.9 1917 826 46.0 21.4 1898 753 21.0 1907 748 22.2 1911 698 Alloy 47 24.8 1765 526 40.1 24.6 1787 492 23.7 1781 463 24.2 1771 478 Alloy 48 16.2 1890 1108 55.0 17.0 1926 1093 15.9 1920 1139 16.4 1899 1073 Alloy 49 16.4 2002 1247 61.5 15.4 1961 1225 16.0 2011 1276 16.3 1990 1275 Alloy 50 16.9 1853 1259 64.9 15.4 1859 1265 15.7 1816 1195 14.6 1833 1313 Alloy 51 18.8 1960 944 51.8 17.8 1963 911 18.1 1947 994 17.3 1915 927 Alloy 52 23.3 1598 366 24.5 20.1 1522 369 25.4 1627 364 25.6 1624 383 Alloy 53 40.3 1407 447 13.1 37.6 1375 441 37.6 1310 437 41.2 1393 444 Alloy 54 19.0 1834 416 36.4 17.8 1827 420 13.0 1720 423 15.4 1811 462 Alloy 55 23.0 1237 462 24.9 18.3 1088 443 21.6 1212 468 22.9 1302 470 Alloy 56 36.8 1039 473 13.2 36.0 1051 497 36.4 1026 480 34.9 1068 514

CASE EXAMPLES Case Example #1 Tensile Properties of the Sheet at 1.2 mm Thickness

The hot band from alloys herein listed in Table 1 was cold rolled to final target gauge thickness of 1.2 mm through multiple cold rolling passes. Cold rolling is defined as rolling at ambient temperature. Hot band material was media blasted prior to cold rolling to remove surface oxides which could become embedded during the rolling process. The resultant cleaned sheet material was rolled using a Fenn Model 061 2 high rolling mill. Sheet was fed through the rolls, and the roll gap is reduced for each subsequent pass until the desired thickness is achieved or the material hardens to the point where additional rolling does not achieve significant reduction in thickness. Annealing was applied before next rolling to recover ductility. Multiple cycles of cold rolling and annealing might be applied. Once the final gauge thickness was reached, samples were cut from each cold rolled sheet by wire EDM. Tensile properties were measured on an Instron mechanical testing frame (Model 3369), utilizing Instron's Bluehill control and analysis software. All tests were run at ambient temperature in displacement control. Samples were tested under displacement control at a constant displacement rate of 0.036 mm/s, which resulted in sample strain rates, calculated from video strain measurements, ranging from 4.4×10⁻⁴ s⁻¹ to 6.8×10⁻³ s⁻¹, depending on several factors including, but not always limited to mechanical compliance, sample slippage, and settling of the wedge action grips used.

Tensile properties of 1.2 mm thick sheet from alloys herein after cold rolling are listed in Table 4. The ultimate tensile strength values after cold rolling is in a range from 1360 to 2222 MPa; yield strength varies from 1006 to 2073 MPa and tensile elongation is recorded in the range from 4.2 to 37.2%. The magnetic phases volume percent was measured by Feritscope in a range from 1.6 to 84.9 Fe % in a cold rolled sheet depending on alloy chemistry.

TABLE 4 Tensile Properties of 1.2 mm Thick Sheet from the Alloys After Cold Rolling Ultimate Magnetic Cold Tensile Tensile Yield Phases Volume Rolling Elongation Strength Strength Percent Reduction Alloy (%) (MPa) (MPa) (Fe %) (%) Alloy 1 20.5 1712 1114 31.4 38.0 20.4 1712 1131 15.0 1705 1073 Alloy 2 21.8 1603 1135 27.8 39.7 23.2 1612 1111 25.7 1589 1120 Alloy 3 29.9 1540 1140 34.6 36.9 28.9 1551 1118 29.5 1553 1234 Alloy 4 25.4 1645 1192 43.3 39.2 25.6 1650 1217 26.4 1639 1381 Alloy 5 17.1 1758 1335 44.9 38.3 18.5 1764 1321 17.8 1764 1285 Alloy 6 22.5 1686 1018 31.3 35.3 22.9 1685 1072 21.6 1687 1042 Alloy 7 16.9 1874 1666 66.5 35.7 14.8 1881 1680 13.3 1875 1360 Alloy 8 10.7 1835 1068 53.4 35.4 16.4 1859 1086 17.5 1860 1336 Alloy 9 19.7 1742 1014 37.0 36.0 17.5 1732 1104 18.2 1732 1120 Alloy 10 20.1 1715 1038 40.3 35.1 20.5 1716 1280 20.5 1729 1173 Alloy 11 13.9 1893 1320 69.9 32.7 15.0 1906 1467 15.6 1875 1536 Alloy 12 5.5 2125 1913 57.0 33.8 5.9 2116 1720 4.2 2114 1675 Alloy 13 22.8 1500 1182 25.6 36.5 24.0 1523 1204 23.9 1518 1098 Alloy 14 18.6 1790 1561 52.1 34.5 20.2 1793 1436 17.9 1726 1491 Alloy 15 5.0 2051 1784 58.9 37.3 6.2 2073 2000 6.3 2057 1957 Alloy 16 19.9 1700 1413 42.0 36.9 19.7 1689 1436 21.1 1704 1302 Alloy 17 20.1 1765 1379 45.9 36.0 20.2 1759 1306 17.2 1764 1374 Alloy 18 20.6 1708 1388 44.1 37.3 20.0 1721 1326 18.9 1709 1369 Alloy 19 18.9 1810 1213 44.8 38.0 19.3 1807 1324 19.2 1806 1260 Alloy 20 15.1 1864 1404 54.8 38.3 16.2 1884 1461 17.1 1879 1512 Alloy 21 18.6 1780 1374 54.9 34.1 18.0 1785 1414 18.6 1786 1006 Alloy 22 17.3 1759 1356 43.9 38.0 21.3 1736 1196 18.8 1757 1304 Alloy 23 19.3 1718 1240 41.3 37.4 20.4 1728 1283 19.0 1727 1271 Alloy 24 22.0 1709 1136 36.8 37.5 12.6 1695 1256 14.8 1706 1258 Alloy 25 19.8 1715 1326 42.6 33.5 20.2 1704 1320 21.0 1700 1316 Alloy 26 18.8 1822 1377 48.5 35.6 17.9 1816 1327 Alloy 27 30.7 1442 1146 12.6 34.5 29.9 1360 1108 24.2 1428 1164 Alloy 28 21.0 1625 1215 20.6 37.5 26.6 1646 1187 23.9 1602 1172 Alloy 29 18.1 1718 1483 58.3 38.8 18.6 1712 1454 19.4 1720 1407 Alloy 30 17.7 1770 1335 44.6 39.9 17.7 1764 1430 17.9 1765 1515 Alloy 31 17.5 1834 1524 49.4 40.5 16.9 1831 1707 16.0 1837 1578 Alloy 32 15.7 1890 1442 50.2 41.1 14.8 1897 1563 15.4 1886 1676 Alloy 33 15.4 1891 1533 56.3 38.2 16.3 1889 1604 15.8 1895 1419 Alloy 34 10.9 1519 1249 1.6 39.0 9.4 1515 1037 10.8 1519 1345 Alloy 35* 16.2 2222 1693 73.7 19.6 16.4 2216 1735 16.2 2217 1657 Alloy 36 16.4 1641 1116 29.6 36.7 20.6 1604 1187 19.1 1623 1295 Alloy 37 7.1 1949 1617 84.9 36.3 6.6 1977 1824 6.5 1975 1834 Alloy 38 7.0 1727 1539 3.8 43.0 9.7 1721 1373 10.0 1717 1490 Alloy 39 16.0 1869 1289 50.0 36.5 19.0 1840 1471 19.0 1837 1245 Alloy 40 15.6 1917 1238 45.8 37.4 17.2 1913 1361 17.7 1917 1192 Alloy 41 28.6 1452 1121 26.4 39.2 31.1 1445 1101 31.1 1431 1231 Alloy 42 21.4 1673 1516 35.5 44.9 23.1 1686 1519 22.9 1675 1509 Alloy 43 37.2 1656 1313 38.1 39.2 31.2 1650 1304 30.0 1667 1332 Alloy 44 19.6 2091 1623 57.8 37.1 20.4 2095 1653 20.1 2098 1656 Alloy 45 21.7 2028 1331 50.9 40.9 22.8 2014 1313 22.6 2017 1334 Alloy 46* 18.5 2095 1755 62.2 29.3 18.5 2100 1754 19.3 2106 1773 Alloy 47 14.7 2024 1482 57.8 36.2 21.3 2020 1496 19.4 2024 1473 Alloy 48* 11.7 2197 2029 72.6 20.7 11.6 2197 1993 10.6 2197 2010 Alloy 49 11.1 2138 1985 76.6 11.3 11.6 2137 1948 11.1 2138 1964 Alloy 50* 8.7 2166 2041 83.3 26.7 8.0 2168 2060 8.5 2170 2073 Alloy 51* 11.9 2197 1904 68.4 21.0 11.0 2194 1917 12.0 2190 1897 Alloy 52 15.2 2071 1788 55.1 34.6 16.4 2068 1764 13.8 2073 1781 Alloy 53 22.1 1908 1630 45.3 38.5 23.5 1911 1584 24.3 1908 1590 Alloy 54* 7.9 2104 1675 57.5 30.3 5.8 2032 1673 7.4 2083 1646 Alloy 55 8.2 1738 1479 44.5 38.1 11.0 1812 1497 11.5 1829 1486 Alloy 56 28.8 1705 1386 32.9 39.4 32.5 1703 1452 28.2 1747 1443 *Thickness of 1.2 mm was not achieved in these alloys due to high strength and equipment limitations. Alloys are tested at thickness from 1.3 to 1.4 mm.

The samples were annealed under conditions intended to simulate the thermal exposure expected during an industrial continuous annealing process representing final treatment of sheet material in Step 2 in FIG. 1, FIG. 2 and FIG. 3. Samples were loaded into a furnace preheated to 850° C., and held at temperature for 10 minutes, wrapped in foil and held under a steady argon flow to minimize oxidation damage. Samples were removed at temperature and allowed to air cool to ambient temperature before testing. Tensile properties were measured on an Instron mechanical testing frame (Model 3369), utilizing Instron's Bluehill control and analysis software. All tests were run at ambient temperature in displacement control at a constant displacement rate of 0.036 mm/s, which resulted in sample strain rates, calculated from video strain measurements, ranging from 4.4×10⁻⁴ s⁻¹ to 6.8×10⁻³ s⁻¹, depending on several factors including, but not always limited to mechanical compliance, sample slippage, and settling of the wedge action grips used.

Tensile properties of 1.2 mm sheet from alloys herein after annealing are listed in Table 5. The ultimate tensile strength values of the annealed sheet from alloys herein is in a range from 725 to 2072 MPa; yield strength varies from 267 to 1428 MPa and tensile elongation is recorded in the range from 12.8 to 76.9%. The relative magnetic phases volume percent was measured by Feritscope with the magnetic phases volume percent of 0.2 to 68.2 Fe % depending on alloy chemistry.

Properties of cold rolled and annealed sheet from Alloys herein corresponds to Step 2 in FIG. 1, FIG. 2 and FIG. 3.

TABLE 5 Tensile Properties of 1.2 mm Thick Sheet from the Alloys after Annealing Ultimate Average Tensile Tensile Yield Magnetic Phases Elongation Strength Strength Volume Percent Alloy (%) (MPa) (MPa) (Fe %) Alloy 1 55.7 1267 473 1.2 52.0 1242 451 56.1 1248 470 57.7 1277 463 Alloy 2 62.4 1162 491 1.3 59.4 1179 469 61.8 1193 477 62.6 1172 531 Alloy 3 61.2 1165 319 0.9 64.2 1153 320 63.2 1145 302 Alloy 4 61.9 1218 350 1.2 58.6 1201 344 51.4 1223 341 64.1 1208 337 Alloy 5 52.0 1239 393 0.7 54.6 1235 398 53.9 1227 442 Alloy 6 61.3 1194 426 1.0 61.0 1238 450 53.9 1208 417 Alloy 7 31.5 1440 338 10.8 33.1 1475 322 32.7 1483 312 33.1 1481 347 31.3 1461 323 32.1 1472 332 Alloy 8 56.2 1269 430 0.9 61.3 1225 471 56.6 1277 421 Alloy 9 56.2 1269 430 1.0 61.3 1225 471 56.6 1277 421 Alloy 10 54.3 1238 412 0.7 56.9 1192 397 59.9 1238 412 Alloy 11 41.3 1437 420 0.9 44.3 1434 424 41.7 1464 412 43.5 1419 417 Alloy 12 29.9 1574 379 2.3 30.1 1571 374 29.7 1579 373 Alloy 13 62.9 1097 367 1.0 69.8 1121 375 68.9 1103 368 Alloy 14 47.1 1363 372 1.1 46.7 1384 376 43.8 1365 366 42.6 1386 370 Alloy 15 24.2 1528 305 20.0 24.8 1535 308 26.0 1534 315 Alloy 16 54.6 1243 376 0.9 55.0 1258 422 54.8 1237 376 55.9 1249 382 Alloy 17 53.3 1333 406 0.4 50.0 1304 410 53.6 1289 403 51.1 1323 392 Alloy 18 55.2 1238 420 0.6 58.7 1198 414 56.1 1235 425 53.2 1244 417 Alloy 19 50.4 1273 451 0.8 50.5 1278 416 51.0 1348 436 53.2 1299 414 Alloy 20 43.4 1378 408 1.0 44.7 1362 406 34.1 1308 429 28.7 1175 397 Alloy 21 52.7 1298 340 1.6 46.9 1326 348 35.4 1270 349 48.6 1324 350 Alloy 22 54.8 1273 399 0.9 54.1 1268 397 56.1 1297 408 Alloy 23 59.3 1239 403 0.3 59.5 1296 407 56.2 1255 409 Alloy 24 60.0 1235 423 0.7 60.1 1247 432 61.8 1237 428 Alloy 25 56.8 1255 376 0.3 51.6 1244 380 57.0 1217 382 Alloy 26 51.0 1305 417 0.7 50.0 1311 432 51.1 1319 433 Alloy 27 59.7 1033 387 0.5 53.8 975 368 63.0 1017 377 Alloy 28 41.3 1128 480 0.2 45.7 1168 482 47.2 1168 485 47.0 1168 492 Alloy 29 58.4 1218 370 1.1 50.7 1250 386 57.3 1251 378 55.1 1239 382 Alloy 30 49.0 1297 383 1.1 54.0 1318 445 53.3 1304 381 Alloy 31 45.0 1299 382 1.2 47.5 1328 383 52.3 1328 392 50.8 1328 397 Alloy 32 50.9 1380 420 1.1 43.1 1373 391 52.4 1371 390 Alloy 33 45.6 1399 388 1.1 36.3 1383 396 44.2 1418 398 34.4 1380 410 Alloy 34 64.7 993 484 0.3 66.1 997 491 66.2 994 481 66.3 994 491 Alloy 35* 14.0 2066 792 60.1 14.0 2072 775 14.5 2072 745 13.6 1971 775 Alloy 36 50.1 1175 483 0.9 50.9 1161 472 50.8 1190 471 Alloy 37 13.2 1621 635 68.2 13.2 1607 645 13.5 1586 574 13.4 1600 644 Alloy 38 60.3 1134 499 0.5 58.2 1141 500 60.4 1139 500 64.2 1138 490 Alloy 39 20.2 929 372 3.0 16.2 725 375 19.4 827 382 21.9 941 362 Alloy 40 15.6 759 379 0.6 17.9 888 420 17.0 839 368 18.0 849 431 Alloy 41 53.0 889 312 1.4 43.5 893 311 50.9 882 315 Alloy 42 68.5 1126 381 1.4 74.7 1105 370 75.2 1154 384 76.9 1141 375 Alloy 43 51.3 1285 344 3.0 50.6 1296 352 41.2 1132 341 62.4 1284 342 Alloy 44 12.8 1898 1269 57.5 14.0 1959 1272 14.1 1962 808 14.1 1961 1235 Alloy 45 16.1 1875 540 51.3 15.5 1888 517 16.0 1867 514 15.4 1878 546 Alloy 46* 14.2 2007 1125 59.0 14.3 2004 879 14.6 1998 866 13.5 2000 903 Alloy 47 13.3 1888 1217 53.6 14.6 1877 1240 13.0 1884 1237 14.2 1892 1253 Alloy 48* 15.2 1853 1128 59.1 15.0 1854 1130 15.4 1852 1131 Alloy 49 15.3 1982 1409 65.1 15.6 1998 1399 14.2 1964 1381 15.4 2008 1428 Alloy 50* 14.6 1833 1307 64.8 14.7 1846 1325 14.5 1844 1271 14.4 1844 1387 Alloy 51* 15.9 1940 1297 57.5 15.4 1937 1209 16.0 1929 1223 Alloy 52 25.4 1722 314 23.2 24.6 1719 267 23.8 1706 276 28.6 1717 319 Alloy 53 47.3 1492 421 5.0 44.1 1514 420 38.4 1478 401 48.9 1488 420 Alloy 54* 17.7 2012 569 50.8 17.1 2009 1053 17.0 2017 1158 16.8 2023 1140 Alloy 55 35.0 1627 351 20.6 39.6 1656 350 33.0 1657 358 Alloy 56 42.2 1265 388 6.4 41.2 1288 391 45.9 1345 395 47.7 1289 387 *Thickness of 1.2 mm was not achieved in these alloys due to high strength and equipment limitations. Samples were tested at thickness from 1.3 to 1.4 mm.

This Case Example demonstrates properties of the sheet material from alloys herein with thickness of 1.2 to 1.4 mm and tested at strain rates from 4.4×10⁻⁴ s⁻¹ to 6.8×10⁻³ s⁻¹.

Case Example #2 Sheet Thickness Effect on Tensile Properties of Alloy 2

The hot band from Alloy 2 was cold rolled into sheets with different thicknesses through multiple cold rolling passes. Once the targeted gauge thickness was reached, samples were cut from each cold rolled sheet by wire EDM. The samples were annealed under conditions intended to simulate the thermal exposure expected during an industrial continuous annealing process. Samples were wrapped in stainless steel foil to prevent oxidation and loaded into a preheated furnace at 850° C. Samples were left in the furnace for 10 minutes while the furnace purged with argon before being removed and allowed to air cool. The only exception was the final anneal for the 4.8 mm material. This anneal was an 850° C. 20 min air cooled anneal, as opposed to the 10 minute anneal used for every other thickness. The purpose of this change was to allow more time for the material to heat up as it was a much thicker sample. Tensile properties were measured on an Instron mechanical testing frame (Model 5984), utilizing Instron's Bluehill control and analysis software. All tests were run at ambient temperature in displacement control. All samples were tested at displacement rate of 0.125 mm/s, which resulted in sample strain rates, calculated from video strain measurements, ranging from 9.1×10⁻⁴ s⁻¹ to 1.9×10⁻³ s⁻¹ depending on several factors including, but not always limited to mechanical compliance, sample slippage, and settling of the wedge action grips used.

The results of tensile testing of the sheet from Alloy 2 processed to different thicknesses are listed in Table 6. In samples with thickness less than 1.2 mm representing Step 3 in FIG. 1, tensile strength varies from 1100 to 1190 MPa and yield strength is between 408 and 439 MPa. FIG. 4 and FIG. 5 show the tensile properties of Alloy 2 sheet as a function of the thickness. Average tensile elongation is 53.7% for Alloy 2 sheet with thickness varying from 0.20 to 1.03 mm (as compared to average of 61.5% in Alloy 2 sheet with thickness of 1.2 mm). Slightly higher elongation is observed up to 66.4% in thicker sheet samples above 1.2 mm. The stress-strain curves in FIG. 6 also demonstrate consistent properties and stress-strain behavior in sheet samples with different thicknesses.

TABLE 6 Sheet Thickness Effect on Tensile Properties of Alloy 2 Ultimate Yield Sample Thickness Tensile Elongation Tensile Strength Strength (mm) (%) (MPa) (MPa) 4.82 54.7 1164 377 4.81 60.2 1202 380 4.79 57.8 1203 350 3.05 57.5 1222 453 3.04 66.4 1183 462 3.01 65.8 1190 450 1.03 52.3 1190 411 1.03 53.8 1179 410 1.02 62.1 1170 408 1.00 57.6 1186 415 0.77 54.8 1184 432 0.77 53.8 1178 430 0.75 52.2 1180 428 0.53 55.3 1148 417 0.53 53.5 1106 423 0.53 51.7 1163 422 0.41 51.6 1111 438 0.41 53.9 1120 439 0.41 51.1 1100 439 0.21 51.2 1125 434 0.20 51.0 1124 434

This Case Example demonstrates that high ductility maintained in the sheet with thickness in a wide range from 4.8 mm down to as small as 0.2 mm. Reduction in sheet thickness below 1.2 mm results in an average total elongation that is no less than that in the sheet with 1.2 mm thickness and above minus 7.8%. An average ultimate tensile strength is 25 MPa less than that in the corresponding sheet with 1.2 mm thickness and above and average yield strength is 67 MPa less.

Case Example #3 Thickness Effect on Tensile Properties of Sheet from Selected Alloys

The hot band from Alloy 1, Alloy 27, and Alloy 37 was cold rolled in to sheets with different thicknesses less than 1.2 mm through multiple cold rolling passes. Once the targeted gauge thickness was reached, samples were cut from each cold rolled sheet by wire EDM. The samples were annealed under conditions intended to simulate the thermal exposure expected during an industrial continuous annealing process representing final treatment at sheet processing in Step 2 in FIG. 1. Samples were wrapped in stainless steel foil to prevent oxidation and loaded into a preheated furnace at 850° C. Samples were left in the furnace to 10 minutes while the furnace purged with argon before being removed and allowed to air cool. Tensile properties were measured on an Instron mechanical testing frame (Model 5984), utilizing Instron's Bluehill control and analysis software. All tests were run at ambient temperature in displacement control. All samples were tested at the displacement rate of 0.125 mm/s, which resulted in sample strain rates, calculated from video strain measurements, ranging from 9.1×10⁻⁴ s⁻¹ to 1.9×10⁻³ s⁻¹ depending on several factors including, but not always limited to mechanical compliance, sample slippage, and settling of the wedge action grips used.

The results of tensile testing of the sheet from the alloys processed to different thicknesses are listed in Table 7 representing Step 3 in FIG. 1. For Alloy 1, tensile elongation is measured in the range from 44.9 to 51.1%, for Alloy 27 in the range from 63.8 to 73.8%, and for Alloy 37 in the range from 6.0 to 7.0%. Tensile elongation as a function of the sheet thickness is illustrated in FIG. 6 for the selected alloys. FIG. 8 and FIG. 9 show the yield strength and ultimate tensile strength of the sheet with different thicknesses for the selected alloys. The ultimate tensile strength is in a range from 1203 to 1269 MPa in Alloy 1 sheet, from 972 to 1067 MPa in Alloy 27 sheet, and from 1493 to 1614 MPa in Alloy 37 sheet. Yield strength varies from 375 to 444 MPa in Alloy 1 sheet, from 367 to 451 MPa in Alloy 27 sheet, and from 612 to 820 MPa in Alloy 37 sheet.

TABLE 7 Tensile Properties of the Sheet from Selected Alloys at Thickness < 1.2 mm Tensile Ultimate Tensile Yield Thickness Elongation Strength Strength Alloy (mm) (%) (MPa) (MPa) Alloy 1 0.52 49.2 1269 444 0.52 51.1 1247 440 0.52 48.1 1203 433 0.76 49.8 1241 406 0.76 50.7 1238 409 0.77 44.9 1247 413 0.99 46.8 1253 375 1.01 45.4 1262 381 1.01 46.7 1251 384 1.02 47.6 1255 396 1.03 50.3 1237 384 1.04 45.6 1246 396 Alloy 27 0.21 63.8 1067 440 0.21 64.9 1063 445 0.37 67.1 1039 429 0.38 68.6 1040 427 0.38 69.5 1022 425 0.51 68.2 1060 451 0.52 68.5 1056 449 0.75 71.8 1019 413 0.76 71.1 1012 412 1.02 72.9 972 367 1.03 73.8 1005 380 1.04 71.7 1001 369 Alloy 37 0.30 6.4 1579 727 0.32 6.0 1493 782 0.32 6.5 1523 790 0.50 6.6 1603 820 0.51 6.3 1614 754 0.51 6.0 1602 775 0.75 6.7 1602 710 0.77 6.6 1590 612 0.99 6.9 1589 659 1.01 6.8 1588 673 1.01 6.9 1596 648

This Case Example demonstrates that tensile ductility of alloys herein is maintained even at sheet thickness as small as 0.2 mm demonstrating an average total elongation no less than that in the corresponding sheet with 1.2 mm thickness and above minus 7.3%. An average ultimate tensile strength is a range of ±35 MPa of that in the corresponding sheet with 1.2 mm thickness and above with the yield strength in a range of ±98 MPa.

Case Example #4 Microstructure in Sheet from Selected Alloys at Different Thicknesses

The hot band from Alloy 1, Alloy 2, Alloy 27, and Alloy 37 was cold rolled in to sheets with different thicknesses less than 1.2 mm through multiple cold rolling passes. Once the targeted gauge thickness was reached, samples were cut from each cold rolled sheet by wire EDM. The samples were annealed under conditions intended to simulate the thermal exposure expected during an industrial continuous annealing process. Samples were wrapped in stainless steel foil to prevent oxidation and loaded into a preheated furnace at 850° C. The microstructures of the cold rolled and annealed state were studied by SEM to show the structural change during processing. To prepare SEM samples, pieces were cut by EDM from the sheet and mounted in epoxy, and the sheet cross-sections were polished progressively with 9 μm, 6 μm and 1 μm diamond suspension solution, and finally with 0.02 μm silica. The SEM study was conducted using an EVO-60 scanning electron microscope manufactured by Carl Zeiss SMT Inc.

FIG. 10 shows microstructures in Alloy 1 sheet samples with different thicknesses. Cold rolled structure is shown in FIG. 10a and FIG. 10c in the center of the sheet with thickness of 0.7 and 0.5 mm, respectively. The cold rolled sample bears the highly deformed microstructure in which grain boundaries are difficult to see. The microstructure in these sheet samples after annealing is shown in FIG. 10b and FIG. 10d represented by the recrystallized structure with equiaxed grains and clear grain boundaries.

FIG. 11 shows microstructures in Alloy 2 sheet samples with different thicknesses. Cold rolled structure is shown in FIG. 11a , FIG. 11c and FIG. 11e in the center of the sheet with thickness of 1.0, 0.5 and 0.2 mm, respectively. The cold rolled sample bears the highly deformed microstructure in which grain boundaries are difficult to see. The microstructure in these sheet samples after annealing is shown in FIG. 11b , FIG. 11d and FIG. 11f represented by recrystallized structure with equiaxed grains and clear grain boundaries.

The structure in the sheet samples from Alloy 27 is similar to Alloy 1 and Alloy 2 and is shown in FIG. 12. The recrystallized microstructure in the sheet from Alloy 27 has fewer twins as compared to other studied alloys, as shown in FIG. 12b , FIG. 12d and FIG. 12 f.

Alloy 37 is a different type of the alloy in which the annealing does not lead to the typical recrystallized structure formation. FIG. 13 shows the structures at the center of the sheet from Alloy 37 with different thicknesses after cold rolling and after cold rolling and annealing. Only a small difference between the cold rolled and the annealed structures is observed. Corresponding samples at different thicknesses have effectively identical structures.

This Case Example demonstrates that microstructure is maintained in alloys herein after annealing of cold rolled sheet independently from the final sheet thickness.

Case Example #5: Strain Rate Effect on Tensile Ductility of the Sheet from Alloy 2

Slabs of Alloy 2 were cast according to the atomic compositions provided in Table 1. Following casting, the slabs were hot rolled through successively smaller roll gaps to produce hot band coils in the range of 2 to 5 mm thick, which were subsequently subjected to cold rolling and annealing cycles until the targeted thickness of approximately 1.4 mm was achieved representing sheet material in Step 2 in FIG. 2. Annealing was done in this case in the temperature range from 950 to 1050° C.

The tensile properties of the material were characterized as a function of strain rate. Tensile samples were tested at 0.0007 s⁻¹, 0.7 s⁻¹, 10 s⁻¹, 100 s⁻¹, 500 s⁻¹ and 1200 s⁻¹ nominal strain rates in the ASTM D638 Type V tensile geometry shown in FIG. 14. Tensile samples tested at strain rates from 0.0007 s⁻¹ to 500 s⁻¹ were tested on an MTS servo-hydraulic test frame. Samples were inserted into grips and load was applied by raising the crosshead at speeds necessary to produce the nominal strain rates. A slack adapter consisting of a cup and cone rod assembly was used at strain rates greater than 1 s⁻¹ to allow the test frame to achieve the targeted constant strain rate prior to applying load to the specimen. An instrumented bar was used at 500 s⁻¹ to mitigate the effects of standing waves in the test apparatus that occurred during high strain rate testing. At 1200 s⁻¹ strain rate, a split Hopkinson bar (SHB) was used. The SHB device was composed of 25.4 mm diameter 7075 Al incident and transmission bars, with the test specimen tightly gripped between the Al bars. Strain gauges were used on the transmission and incident bars to measure strain in the bars. A striker tube was launched around the incident tube towards the striker plate to generate the tensile strain pulse and the strain within the sample was recorded. A schematic diagram of the SHB is provided in FIG. 15.

Strain in the tensile samples was measured by a mechanical extensometer at 0.0007 s⁻¹ and 0.7 s⁻¹ strain rates. Digital Image Correlation (DIC) was used to measure strain for samples tested at 10 s⁻¹, 100 s⁻¹, and 500 s⁻¹. Five tensile samples were tested at all strain rates. In the case of one sample at 0.0007 s⁻¹ strain rate, a malfunction occurred that resulted in the loss of the sample. Two samples tested at 1200 s⁻¹ did not fail during testing.

Measured strain at failure is provided in Table 8. The measured strain is plotted as function of strain rate in FIG. 16. Table 9 provides the average ductility as measured by tensile elongation at failure for each nominal strain rate. Note that the average tensile elongation measured at all strain rates is close to the overall average of 55.5% across all strain rates. At strain rates from 0.0007 s⁻¹ to 500 s⁻¹, the average tensile elongation at failure is within approximately ±3% of the total average of all tests. Tests at 1200 s⁻¹ were measured to possess higher tensile elongation at failure than all other tests, however due to the nature of this test methodology these values may be measured slightly higher than actual values. Ultimate tensile strength is measured in a range from 944 to 1187 MPa with yield strength from 347 to 512 MPa (Table 10).

Tensile properties in Tables 8 through 10 represents sheet material in Step 3 in FIG. 2.

TABLE 8 Tensile Elongation of Alloy 2 Sheet Samples Tested at Different Strain Rates Nominal Strain Strain Elongation at Rate Measurement Measured Strain Rate Failure (s⁻¹) Technique (s⁻¹) (%) 0.0007 Extensometer 0.000803 62.4 0.0007 Extensometer 0.000768 44.6 0.0007 Extensometer 0.000713 44.9 0.0007 Extensometer 0.000749 59.2 0.7 Extensometer 0.644 57.1 0.7 Extensometer 0.682 53.7 0.7 Extensometer 0.632 54.4 0.7 Extensometer 0.634 54.5 0.7 Extensometer 0.650 52.5 10 DIC 5.83 49.5 10 DIC 6.03 50.4 10 DIC 6.07 54.6 10 DIC 6.02 49.5 10 DIC 5.78 54 100 DIC 65.7 55.7 100 DIC 87.9 52.7 100 DIC 88.5 56.2 100 DIC 86.2 54.5 100 DIC 85.4 57.1 500 DIC 438 57.0 500 DIC 442 57.3 500 DIC 440 56.2 500 DIC 414 57.5 500 DIC 425 56.1 1200 SHB 1169 64.9 1200 SHB 1222 67.7 1200 SHB 1152 63.1

TABLE 9 Average Tensile Elongation of Sheet from Alloy 2 at Each Strain Rate Strain Nominal Strain Rate Measurement Elongation at Failure (s⁻¹) Technique (%) 0.0007 Extensometer 52.8 0.7 Extensometer 54.4 10 DIC 52.0 100 DIC 55.2 500 DIC 56.8 1200 SHB 65.2 Overall Average 56.0

TABLE 10 Strength Characteristics of Alloy 2 Sheet Tested at Different Strain Rates Ultimate Nominal Strain Strain Measured Yield Tensile Rate Measurement Strain Rate Strength Strength (s⁻¹) Technique (s⁻¹) (MPa) (MPa) 0.0007 Extensometer 0.000803 375 1159 0.0007 Extensometer 0.000768 356 1151 0.0007 Extensometer 0.000713 365 1171 0.0007 Extensometer 0.000749 371 1187 0.7 Extensometer 0.644 354 1014 0.7 Extensometer 0.682 454 992 0.7 Extensometer 0.632 431 1017 0.7 Extensometer 0.634 416 1024 0.7 Extensometer 0.650 442 1006 10 DIC 5.83 455 989 10 DIC 6.03 422 979 10 DIC 6.07 424 980 10 DIC 6.02 450 975 10 DIC 5.78 347 977 100 DIC 65.7 483 956 100 DIC 87.9 499 944 100 DIC 88.5 488 953 100 DIC 86.2 505 956 100 DIC 85.4 459 948 500 DIC 438 425 1020 500 DIC 442 409 1030 500 DIC 440 500 1010 500 DIC 414 444 1030 500 DIC 425 512 1020 1200 SHB 1169 — 946 1200 SHB 1222 — 965 1200 SHB 1152 — 972

This Case Example demonstrates that tensile ductility of alloys herein is retained across a relatively large range of strain rates of 0.007 to 1200 s⁻¹. A measured average ultimate tensile strength is 62 MPa lower at higher strain rates and average yield strength is 59 MPa lower.

Case Example #6 Strain Rate Effect on Microstructure in the Sheet from Alloy 2

The microstructures of the samples from sheet from Alloy 2 tested at five different strain rates ranging from 0.0007 s⁻¹ to 1200 s⁻¹ (see Case Example #5) were studied by TEM. For TEM study, pieces are cut from the gauge section of deformed samples by diamond saw. Grinding and polishing are then undertaken to make thin foils from the cut pieces. The polishing was conducted progressively with 9 μm, 6 μm and 1 μm diamond suspension solution, and finally with 0.02 μm silica. Foils with thickness of 70 to 80 μm were obtained after the polishing. Discs of 3 mm in diameter were punched from the foils and the final polishing was fulfilled with electropolishing using a twin-jet polisher. The chemical solution used was a 30% Nitric acid mixed in Methanol base. In case of insufficient thin area for TEM observation, the TEM specimens may be ion-milled using a Gatan Precision Ion Polishing System (PIPS). The ion-milling usually is done at 4.5 keV, and the inclination angle is reduced from 4° to 2° to open up the thin area. The TEM studies were done using a JEOL 2100 high-resolution microscope operated at 200 kV.

FIG. 17 shows the bright-field TEM images of the sample tested at 1200 s⁻¹. It can be seen that deformation twins are prominent in the high rate deformed sample which are a forming of twinning which does not occur through mechanical deformation but during heat treatment. The twins are distinct and sharp, suggesting that they are newly formed from the deformation. With twinning being a deformation mode in the sample, phase transformation is reduced since the deformation twins maintain austenitic structure. Twinning as a method of deformation can be seen in the sample deformed at strain rates of 500, 100, 10, and 0.7 s⁻¹, as shown in FIG. 18 through FIG. 21. The sample deformed at strain rate of 0.0007 s⁻¹ has different structure as can be seen in FIG. 22 demonstrating a domination of dislocation with phase transformation during deformation that is evident from the Feritscope measurements in the sample gauges after deformation. As shown in FIG. 23, the magnetic phases volume percent, which correlates to the transformed product phases, is highest in the case of deformation at low strain rate of 0.0007 s⁻¹.

This Case Example demonstrates the alteration of deformation mechanisms during deformation of the alloys herein with higher occurrence of twinning with increasing strain rate. Deformation by twinning at high strain rates suppresses the phase transformation (i.e. means that the total amount of ferrite produced is reduced) allowing to the retention of relatively high tensile ductility of the sheet material in a wide range of strain rates.

Case Example #7 Notch Effect on Tensile Properties of Sheet from Alloy 2

Slabs of Alloy 2 were cast according to the atomic compositions provided in Table 1. Following casting, the slabs were hot rolled through successively smaller roll gaps to produce hot band coils, which were subsequently subjected to cold rolling and annealing cycles until the targeted thickness of approximately 1.4 mm was achieved representing sheet in Step 2 in FIG. 3.

Tensile specimens were cut from the sheet via wire EDM. The specimens had two notches, symmetric at about the center of the width and the length as showed in FIG. 24. Samples were tested in tension with one grip fixed and the other moving at a fixed rate of 0.125 mm/s displacement rate. Tensile properties were measured on an Instron mechanical testing frame, utilizing Instron's Bluehill control and analysis software. All tests were run at ambient temperature in displacement control. A 50 mm gauge length was used centered on the notch. Stresses were calculated based on the nominal width not the notched width (FIG. 24).

Tensile properties of the Alloy 2 sheet samples as a function of notch diameter and notch depth are listed in Table 11. Tensile elongation of notched samples ranged from 12.4% to 40.7%, yield strength ranged from 298 to 420 MPa, and ultimate tensile strength ranged from 636 to 1123 MPa. Effect of notch diameter with constant depth of 0.5 mm on tensile properties of the sheet from Alloy 2 is illustrated in FIG. 25. Changes in tensile properties of the sheet with half circle notches as a function of notch diameter are shown in FIG. 26. This data represents sheet in Step 3 in FIG. 3.

TABLE 11 Tensile Properties of Notched Specimens from Alloy 2 Sheet Notch Strain at Ultimate Tensile Diameter Notch Depth Break Strength Yield Strength (mm) (mm) (%) (MPa) (MPa) 0.35 0.175 22.1 913 407 0.35 0.175 26.6 991 409 0.35 0.175 21.2 909 420 0.5 0.25 17.7 844 416 0.5 0.25 18.9 874 411 0.5 0.25 22.0 923 397 1 0.5 14.4 789 406 1 0.5 17.3 827 386 1 0.5 18.2 862 408 2 1 16.7 802 386 2 1 17.9 839 375 2 1 23.0 875 345 4 2 15.6 764 371 4 2 18.7 816 372 4 2 17.9 811 377 6 3 12.4 636 314 6 3 13.1 646 308 6 3 12.9 651 298 2 0.5 22.8 926 405 2 0.5 26.3 992 405 2 0.5 25.8 992 397 4 0.5 27.4 982 394 4 0.5 32.8 1054 391 4 0.5 31.7 1056 396 6 0.5 34.8 1071 383 6 0.5 40.7 1123 384

This Case Example demonstrates an increase in tensile elongation of the notched samples from alloys herein with increasing notch diameter at constant depth. In the case of increasing depth, average elongation is shown to be independent of the notch depth (half circle).

Case Example #8 Ductile Fracture Surface in Notched Sample after Testing

SEM fracture analysis was performed on selected notched specimens from Alloy 2 sheet after tensile testing (see Case Example #7). Two samples with notch radius of 1.0 and 6.0 mm were selected for examination (Table 12). The SEM study was conducted using an EVO-60 scanning electron microscope manufactured by Carl Zeiss SMT Inc.

TABLE 12 Samples for SEM Analysis Notch Diameter Notch Depth Samples (mm) (mm) 1 1.0 0.5 2 6.0 0.5

In FIG. 27 and FIG. 28, SEM images of fracture surface after tensile testing are shown for Sample 1 and Sample 2, respectively. Images are taken from the center of the fracture cross section and close to the edge. Both samples demonstrated ductile fracture. There is no difference in fracture mode between the center and the edge of the fracture cross section although finer structure is found closer to the edge.

This Case Example demonstrates that notch introduction into the sheet material from alloys herein does not cause brittle catastrophic failure. Notched samples after testing have demonstrated ductile fracture.

The alloys herein may be utilized in variety of applications. For example, the alloys herein may be positioned in vehicular frame, vehicle chassis or vehicle panel. In addition, the alloys herein may be utilized for a storage tank, freight car, or railway tank car. Railway tank cars may specifically include tanks, jacketed tanks or tanks with a headshield. Other applications include body armor, metallic shield, military vehicles, and armored vehicle Such applications apply to the alloys produced according to any one of FIG. 1, FIG. 2 and/or FIG. 3. 

1. A method to retain mechanical properties in a metallic sheet alloy at reduced thickness comprising: a. supplying a metal alloy comprising at least 70 atomic % iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu, or C, melting said alloy, cooling at a rate of <250 K/s, and solidifying to a thickness of 25.0 mm up to 500 mm; b. processing said alloy into sheet form with thickness T₁ with the sheet having a total elongation of X₁ (%), an ultimate tensile strength of Y₁ (MPa), and a yield strength of Z₁ (MPa); c. further processing said alloy into a second sheet with reduction in thickness T₂<T₁ with the second sheet having a total elongation of X₂=X₁±10%, an ultimate tensile strength of Y₂=Y₁±50 MPa, and a yield strength of Z₂=Z₁±100 MPa.
 2. The method of claim 1 wherein said at least 70 atomic percent iron is combined with five or more elements that are selected from Si, Mn, Cr, Ni, Cu, or C.
 3. The method of claim 1 wherein said at least 70 atomic percent iron is combined with all six elements: Si, Mn, Cr, Ni, Cu, and C.
 4. The method of claim 1 wherein the levels of the four elements that are selected are as follows: Si (1.14 to 6.13 atomic percent), Mn (3.19 to 15.17 atomic percent), Cr (0.78 to 8.64 atomic percent); Ni (0.9 to 11.44 atomic percent), Cu (0.37 to 1.87 atomic percent).
 5. The method of claim 1 wherein said alloy formed in step (b), exhibits X₁ (12% to 80%), Y₁ (700 MPa to 2100 MPa), and Z₁ (250 MPa to 1500 MPa).
 6. The method of claim 1 wherein said alloy formed in step (b), exhibits a thickness from 1.2 mm to 10.0 mm.
 7. The method of claim 1 wherein said alloy formed in step (c), exhibits X₂ (2 to 90%), Y₂ (650 MPa to 2150 MPa), and Z₂ (150 MPa to 1600 MPa).
 8. The method of claim 1 wherein said alloy formed in step (c), exhibits a thickness from 0.2 mm to <1.2 mm.
 9. The method of claim 1 wherein said alloy formed in step (c) is positioned in a vehicular frame, vehicular chassis, or vehicular panel.
 10. The method of claim 1 wherein said alloy formed in step (c) is positioned in a storage tank, freight car, or railway tank car.
 11. A method to retain mechanical properties in a metallic sheet alloy at relatively high strain rates comprising: a. supplying a metal alloy comprising at least 70 atomic % iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu, or C and melting said alloy and cooling at a rate of <250 K/s and solidifying to a thickness of 25.0 mm up to 500 mm; b. processing said alloy into sheet form with thickness from 1.2 mm to 10.0 mm with the sheet having a total elongation of X₁ (%), an ultimate tensile strength of Y₁ (MPa), and a yield strength of Z₁ (MPa) when tested at a strain rate S₁; c. deforming the sheet from said alloy at a strain rate S₂>S₁ with the sheet having a total elongation of X₃=X₁±7%, ultimate tensile strength Y₃=Y₁±200 MPa, and yield strength Z₃=Z₁±50 MPa.
 12. The method of claim 11 wherein said at least 70 atomic percent iron is combined with five or more elements that are selected from Si, Mn, Cr, Ni, Cu, or C.
 13. The method of claim 11 wherein said at least 70 atomic percent iron is combined with all six elements: Si, Mn, Cr, Ni, Cu, and C.
 14. The method of claim 11 wherein the levels of the four elements that are selected are as follows: Si (1.14 to 6.13 atomic percent), Mn (3.19 to 15.17 atomic percent), Cr (0.78 to 8.64 atomic percent); Ni (0.9 to 11.44 atomic percent), Cu (0.37 to 1.87 atomic percent).
 15. The method of claim 11 wherein said alloy formed in step (b), exhibits X₁ (12% to 80%), Y₁ (700 MPa to 2100 MPa), and Z₁ (250 MPa to 1500 MPa).
 16. The method of claim 11 wherein the strain rate S₁ is 0.007 s⁻¹ to 0.0001 s⁻¹.
 17. The method of claim 11 wherein said alloy formed in step (c), exhibits X₃ (5% to 87%), Y₃ (500 MPa to 2300 MPa), and Z₃ (200 MPa to 1550 MPa).
 18. The method of claim 11 wherein the strain rate S₂ is >0.007 s⁻¹ to 1200 s⁻¹.
 19. The method of claim 11 wherein said processing in step (c) comprises roll forming, metal stamping or hydroforming.
 20. The method of claim 11 wherein said alloy formed in step (c) is positioned in a vehicular frame, vehicular chassis, or vehicular panel.
 21. The method of claim 11 wherein said alloy formed in step (c) is positioned in a storage tank, freight car, or railway tank car.
 22. The method of claim 11 wherein said alloy formed in step (c) is positioned in body armor, shield, military vehicle, or armored vehicle.
 23. A method to retain mechanical properties in a metallic sheet alloy comprising: a. supplying a metal alloy comprising at least 70 atomic % iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu, or C and melting said alloy and cooling at a rate of <250 K/s and solidifying to a thickness of 25.0 mm up to 500 mm; b. processing said alloy into sheet form with thickness from 1.2 mm to 10.0 mm with the sheet having a total elongation of X₁ (%), an ultimate tensile strength of Y₁ (MPa), and a yield strength of Z₁ (MPa); c. introducing stress concentration sites and then deforming the sheet from said alloy with the sheet having a total elongation of X₄≥0.2X₁ (%), an ultimate tensile strength Y₄≥0.5Y₁ (MPa), and a yield strength Z₄≥0.6Z₁ (MPa).
 24. The method of claim 23 wherein said at least 70 atomic percent iron is combined with five or more elements that are selected from Si, Mn, Cr, Ni, Cu, or C.
 25. The method of claim 23 wherein said at least 70 atomic percent iron is combined with all six elements: Si, Mn, Cr, Ni, Cu, and C.
 26. The method of claim 23 wherein the levels of the four elements that are selected are as follows: Si (1.14 to 6.13 atomic percent), Mn (3.19 to 15.17 atomic percent), Cr (0.78 to 8.64 atomic percent); Ni (0.9 to 11.44 atomic percent), Cu (0.37 to 1.87 atomic percent).
 27. The method of claim 23 wherein said alloy formed in step (b), exhibits X₁ (12% to 80%), Y₁ (700 MPa to 2100 MPa), and Z₁ (250 MPa to 1500 MPa).
 28. The method of claim 23 wherein said processing in step (c) comprises roll forming, metal stamping or hydroforming.
 29. The method of claim 23 wherein said alloy formed in step (c) is positioned in a vehicular frame, vehicular chassis, or vehicular panel.
 30. The method of claim 23 wherein said alloy formed in step (c) is positioned in a storage tank, freight car, or railway tank car.
 31. The method of claim 23 wherein said alloy formed in step (c) is positioned in body armor, shield, military vehicle, or armored vehicle. 